1. Field of the Invention
The present invention relates to devices for rotating documents, and in particular to devices for electronically rotating documents 90.degree. while deskewing the documents using a single variable speed drive roller and an intelligent control algorithm.
2. Description of Related Art
Sheet rotation is fast becoming a highly sought after capability to enable the connection of third party finishing devices (i.e., folders, direct mail systems, etc.) to pre-existing copiers and printers. It is common for finishing devices such as, for example, buckle folders, saddle stitchers, direct mail systems, compiler/staplers, and the like, to require documents to be input with their short edge first. However, it is also common for copiers and printers to output documents with their long edge first. Thus, a document rotation device is needed to rotate documents 90.degree. between the output of the copier or printer and the input of the finishing device.
It is also desirable for a 90.degree. rotation device to be selectively operable to rotate documents since, depending on the size of the documents, some documents are outputted by copiers and printers with their short edge first. A device which selectively rotates documents is also useful for establishing set distinction between a plurality of sets of documents outputted by the copier or printer in a continuous manner. That is, sets of documents can be distinguished from one another by alternately rotating and not rotating consecutive sets.
One problem with current document rotation systems is that they require edge registration guides to control the amount of rotation of the document. Since the documents must be forcibly driven into these edge registration guides, corners and edges of the documents can be damaged. This is particularly the case when the documents are light-weight, delicate sheets. Additionally, the use of edge registration guides increases the possibility of documents becoming jammed in the rotator. Furthermore, if corners or edges of the documents are already damaged or are bent or folded after engagement with the edge registration guides, the documents may not be registered properly.
Thus, it is desirable to use a sheet rotation device which does not require edge registration guides. However, edge registration guides perform a useful function in that they "automatically" correct for skew inaccuracies after rotation of the documents because all documents are registered against the same registration guide which is always in the same orientation. Thus, it is also desirable to provide a sheet rotation device which deskews as well as rotates a document without the use of edge registration guides.
It is known to provide separate devices for deskewing or rotating which accomplish deskewing or rotation with multiple rollers, each being driven at different speeds and/or in opposite directions. These devices use at least two servo systems or stepper motors, to achieve the deskewing or rotating procedure. Servo systems and stepper motors are expensive and also require monitoring and control separate from the monitoring and control provided for the other constant velocity feed rollers located throughout the remainder of the system's document feed path. Thus it is desirable to provide a rotating device which achieves rotation and deskewing with only one servo system or stepper motor.
Xerox Disclosure Journal, Vol. 12, No. 4, p. 205 (July/Aug. 1987) to Huggins discloses apparatus for detecting and correcting document skew. The difference in time between the detection of the lead edge of the document by two spaced rollers is used to calculate the input skew angle of the document. Each of the rollers is driven by a separate stepper motor. Once the amount of input skew is determined, control logic can then be arranged to increase the number of steps made by one of the stepper motors, or decrease the number of steps made by the other stepper motor, or a combined increase and decrease of each of the stepper motors can be used during the time that the paper is being driven by the rollers. The rollers can also be alternately differentially driven for a short time period to laterally move and thus side-register the document.
IBM Technical Disclosure Bulletin, Vol. 14, No. 7, p. 2179 (Dec. 1971) to Groenewald and Towne discloses a document cornering mechanism which utilizes a plurality of rollers and a side registration guide to rotate a document 90.degree..
A Research Disclosure Bulletin dated Nov., 1979, and entitled "Means To Correct Document Skew" discloses a document feeder for use on a copier which corrects for document skew using registration gates and variable speed rollers. The means to correct for document skew is disclosed in conjunction with U.S. Pat. No. 4,076,408 to Reid et al.
U.S. Pat. No. 4,500,086 to Garavuso, assigned to Xerox Corporation, discloses a rotating inverter for rotating documents 180.degree.. Rotation is accomplished by opening and closing two pairs of pivoting nips that are driven in opposite directions. The system does not include deskew, and imparts extremely high accelerations onto the sheet due to the roll actuation scheme used.
U.S. Pat. No. 4,438,917 to Janssen et al discloses a dual motor aligner which utilizes two independently controlled servo motors to deskew documents. A skew is deliberately generated on the sheets before entering the two servo controlled rollers, and two sensors are used to detect the skew and lateral position of the sheet. The velocity profile of the two servo driven rollers is then selected from a look-up table to achieve deskew and side registration. The system does not provide sheet rotation capability other than to correct for skew.
U.S. Pat. No. 4,511,242 to Ashbee et al discloses a machine for deskewing documents using two variable speed rollers. This patent describes a system for utilizing the capabilities of the "Dual Motor Aligner" described in the above-mentioned U.S. Pat. No. 4,438,917. The system uses manual and electrical feedback to relate document skew to copy output skew. The Dual Motor Aligner is then used to compensate by adjusting the copy paper position. In addition, the unit senses and corrects for the skew generated during the feeding of the copy paper. The system does not provide sheet rotation capability.
U.S. Pat. No. 4,971,304 issued Nov. 20, 1990 to Lofthus, entitled "Apparatus and Method for Combined Deskewing and Side Registering", assigned to Xerox Corporation, discloses an apparatus and method for combined deskewing and side registering documents. This apparatus utilizes two variable speed rollers to deskew and side register documents having an initially unknown skew. This system also does not provide sheet rotation capability other than to correct for skew and side edge registration.
U.S. Pat. No. 4,669,719 to Fratangelo, assigned to Xerox Corporation, discloses an apparatus for rotating sheets 90.degree. by contacting the document with a series of free floating balls arranged so that the balls selectively retard one side of the sheet moving along a conveyor as well as with a side registration member. This device relies upon gravity to rotate a sheet and must be arranged so that a sheet moves vertically therethrough.
U.S. Pat. No. 3,240,487 to Templeton discloses an apparatus for deskewing documents by rotating a first set of rollers located downstream of a second set of rollers in a direction opposite to that of the second set of rollers.
U.S. Pat. No. 3,589,808 to DelVecchio, assigned to Xerox Corporation, discloses a xerographic reproducing machine which outputs sheets either short-edge first or long-edge first. A sheet can be rotated 90.degree. by being pivoted about a fixed turning post as it is transferred from a first to a second feed path arranged at an angle of 90.degree. to the first feedpath.
U.S. Pat. No. 3,758,104 to Daily discloses a sheet turning apparatus which rotates sheets 90.degree. by contacting the sheet with two rollers, each being driven at a different constant speed. This system does not compensate for input skew and is insensitive to wear or drifting of the various components.
U.S. Pat. No. 4,082,456 discloses an apparatus for deskewing sheets.
U.S. Pat. No. 4,155,440 to Bogdanski et al discloses a document turning station for rotating documents 90.degree. utilizing a plurality of rollers which rotate at different constant velocities to rotate the document and register the document against a side registration guide. This device does not detect or compensate for input skew and requires registration guides.
U.S. Pat. No. 4,727,402 to Smith, assigned to Xerox Corporation, discloses an apparatus for producing sets of signatures. The present invention can be used with a signature producing device since the completed signatures usually must be rotated 90.degree. prior to being stacked and bound by, for example, stapling, stitching or gluing.
The disclosed apparatus may be readily operated and controlled in a conventional manner with conventional control systems. Some additional examples of control systems for various prior art copiers with document handlers, including sheet detecting switches, sensors, etc., are disclosed in U.S. Pat. Nos.: 4,054,380; 4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401; 4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344; 4,284,270, and 4,475,156. It is well known in general, and preferable, to program and execute such control functions and logic with conventional software instructions for conventional microprocessors. This is taught by the above and other patents and various commercial copiers. Such software will of course vary depending on the particular function and the particular software system and the particular microprocessor or microcomputer system being utilized, but will be available to or readily programmable by those skilled in the applicable arts without undue experimentation from either verbal functional descriptions, such as those provided herein, or prior knowledge of those functions which are conventional, together with general knowledge in the software and computer arts. Controls may alternatively be provided utilizing various other known or suitable hardwired logic or switching systems.
All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features, and/or technical background.